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abstraction > mathematical concept > number > quantity > radiation measurement > spectral feature > spectral line > emission line

emission line
subject			fact

emission line	has antonym absorption line
	has definition Bright line superposed on a continuous spectrum. Can be produced in the laboratory by a glowing gas under low pressure.
	has definition Bright lines produced in a spectrum by a luminous source, such as a star or a bright nebula.
	is a kind of spectral line
spectral line	has transition
	has equivalent width
spectral feature	has wavelength
	has width
	occurs in
	has species
radiation measurement	has unit radiation unit
number	has value

Kinds of emission line :

• coronal green line (5 facts) - An emission line of Fe XIV, the strongest line in the solar corona.
• forbidden line (3 kinds, 12 facts) (nebular line) - Spectral line emitted from a metastable state (q.v.), or those which have a very low probability (10^-9-10^-10) of occurrence. They appear at particle densities ≤ 10⁸ cm^-3. All forbidden lines have low excitation potentials. Forbidden lines are designated by enclosing them in brackets, e.g., [O II].
• inverse P Cygni line (2 facts) - An emission line in which the emission is on the violet side of the absorption. It is usually interpreted to mean infall of matter.
• K alpha (2 facts) - A spectral line in the X-ray region (α = 0.334 Å), produced by the transition between the lowest level of the K shell and the lowest level of the L shell.
• main lines (2 facts) - The transitions that emit radiation at 1665 and 1667 mhz of an OH source.
• radio recombination line (2 facts) - Radio recombination lines are the result of electron transitions between high-n (n > 50) levels in an atom or ion.
• semi-forbidden line (2 facts) - Spectral lines from "semiforbidden" transitions, i.e., those whose transition probabilities are perhaps 1 in 10⁶ instead of about 1 in 10⁹ for forbidden transitions. One bracket - e.g., [C III] - is used to indicate semiforbidden lines.